5.1 has a lot of fixes over 5.0. (5.0.1 and 5.0.2 still have bugs.) 5.1 has been released by Android, and by Samsung for a few devices. When will it be released by your carrier for your device? No one can say. Even if they could, updates are rolled out slowly, so as to not bomb the internet with millions of updates at once, so if it's released by your carrier for your device today, you may not get yours for a few months. Or you might get it tomorrow. Anyone making a guess as to when anyone will get any update is just wasting bandwidth.